Funny, I had something similiar happen. I could find nothing about it, but after a careful look I noticed some of my transitions had reset themselves to default settings.
My solutions in order of agony:
1. Shut down program and restart. 2. Reboot computer. 3. Uninstall Vegas and reinstall (very important to uninstall first.) 4. Format drive and reinstall Windows.
If solution 3 fails be sure to lock all your guns up and give the key to somebody else before poceeding to #4..